Flame control device



Patented Jan. 23, 1951 FLAME CONTROL DEVICE Mortimer 'ArSchultz andGeorge W. Nagel, Pitts- "burgh, Pa., assignors to Westinghouse ElectricCorporation, East Pittsburgh, Pa., a corporationof PennsylvaniaApplication April 1, 1948, Serial No. 18,336

14 Claims. .1

Our inventio'irrelates to electric dischargeapparatus and it hasparticular relation to flameresponsive discharge apparatus.

A flame control system constructed and oper ated in accordance with theprior art of which we are aware is disclosed in an application, SerialNo. 792,743, flled December 19, 1947, to George W. Nagel, and assignedto "Westinghouse Electric Corporation. This system includes an electricdischarge device of the cold-cathode ignition-electrode type which isconnected to control the supply of fuel toa burner. The firing electrodeof this device is connected to a flame probe which may be connected tothe anode terminal of the power supply through the ionized path of aflame. The-firing electrode isalso connected to the cathode of thedevice through :-a high impedance. The device becomes conductive whenthere is a flame in the burner.

To render the discharge device conductive, a substantial potential ofthe order of 50 volts must be impressed between its firing electrode andits cathode. This potential is derived from the power supply whichordinarily has a magnitude of the order of -115 volts. The impedancebetween the firing electrode and the cathode of the dischargedevicemust, thereforebe equal to the flame impedance. The latter is ofthe order of 20 megohms. .If an impedance of this order is to bemaintained between the firing electrode and the cathode of the dischargedevice, the electrode terminals of the discharge device must be properlyinsulated. The cost of such a discharge device is, therefore, relativelyhigh-exceedin'g $1.00. The circuit components associated with thedischarge device and its socket must also be designed to maintain the 20.megohm impedance. Provisions must also be included to preclude dust.deposited on the-components or the socket from reducing this impedance.In apparatus such as a clothes'dryer to'be used in the kitchen of a homein an industrial city like Pittsburgh, these requirements may constituteimportant cost factors.

It is accordingly an object of our invention to provide-a flame-controlsystem including an electric discharge device in which the impedancebetween the control electrode and one of the main electrodes oftheadischarge device shall be relatively small.

Another iobject 'of our invention :is to provideia flame control systemwhich :shall be "substan- "tially less costly than zthe=system=including:an electric discharge device of the cold-cathodeignition-electrode type, such as .disclosed in the above-entitled Nagelapplication.

A-further object of ourinvention is'to provide a flame control systemincluding'an electric dis-' vide a transformerless flame control systemincluding an electric discharge device of thehotcathode type.

Another ancillary object of our invention is to provide a flamecontrolsystemincluding an'electric .dischargedevice wherein theimpedance between the control electrode .and the cathode .of theelectric discharge .deviceshall be :small compared to theiflameimpedance.

'A further ancillary object of our invention is to provide a circuitincluding an electric discharge device of the hot-cathode type .but notincluding a heating transformer for the cathode.

Our invention arises from the realization that a grid-controlledhot-cathode tube of the highvacuum type produces a relatively largevariation in anode current inrespons'e to a relatively small variationin grid potential. We have found that in such a tube, a swing ofapproximately 10 to 20 volts in the cathode potential produces avariation of 15 to 25 milliamperes in the plate current. A-swing of 20volts in potential can be produced across'a resistor .of the orderof 5megohms connected in series with a 20 megohm resistor between theterminals of a volt power supply. Accordingly, in a flame control systemincluding a high-vacuum hot-cathode tube, the grid resistor may be ofthe order of 5 megchms. In the preferred practice of our invention, weaccordingly provide a flame control system including a discharge deviceof the hot-cathode type.

Our flame control system is particularly designed for use in a clothesdryer. In a dryer it is essential that the discharge device be capableof conducting plate current immediately after the starting switch of thedryer is closed by the operator. We have found that a hot-cathode tubewith a directly-heated cathode such as a 3A4, for example, operatessatisfactorily in such a drying system. The cathode of such a tubereaches a temperature at which it is properly emissive only one or twoseconds after power is applied to it. Accordingly, an important specificfeature of our invention is the inclusion in a flame controlsystem of adirectly-heated hot-cathode discharge device.

Flame control systems, whether for dryers or particularity in theappended claims.

for control heaters for homes are ordinarily supplied from a comm rcial110 volt source. Since the cathode of a hot-cathode tube operates at apotential substantially lower than that of the supply, the inclusion ofa hot -cathode discharge device in a flame control system raises a prob.lem as to cathode heating supply. A r-cathode transformer should beavoided if practicable lee-- cause it constitutes an undesirable item ofcost. In accordance with another specific aspect of our invention, thecathode of the discharge device in our system is energized from theanode supply, through a drop resistor which absorbs the excessivevoltage.

In accordance with a further aspect of our in vention, we provide asystem including a hotcathode discharge device of the indirectlyheatedtype. The time required for heating the cathode of this discharge devicein the use of this system is shortened by initially impressing on thecathode a substantially higher potential than its rated potential. Thispotential is impressed by operation of the initiating push button andthe potential is reduced to the rated magnitude by actuation of therelay which is controlled from the discharge device.

Another feature of our invention can be conveniently explained byreference to Yates Patent 2,295,885. In the system shown in Fig. 1 ofthis patent the power line L1 is grounded at G and the gas line to theburner is grounded at G. The grounded gas line constitutes one flameprobe and the rod E the other. Yates does not indicate the character ofhis line L1. If it is a line of a commercial power supply, such as isused in energizing dryers and domestic burners, the ground G is providedby the power company and cannot be charged by the operator of a dryer orburner. The operator of a dryer or burner including a flame controlsystem such as Yates, determines the polarity of the electrodes of thedischarge device on inserting the power plug. If it is inserted properlythe anode is connected to the ground as shown by Yates; if it isinserted improperlythe cathode is connected to ground. In the lattercircumstance the device T will not become conductive when the flame isignited since its only affect is to connect the starting anode toground--that is to impress the same potential on the starting anode andcathode. The provision of asymmetric plugs is not practicable becausesuch plugs would require asymmetric receptacles unavailable in manyhomes.

In accordance with our invention we provide a system including a pair offlame probes neither of which is grounded-that is neither is at thepotential of either of the power company supply lines. The magnitudesand polarities of the potentials of both probes is properly related tothe magnitudes and polarities of the potentials impressed on theelectrodes of the discharge device regardless of the manner in which theplug of the system is inserted in the power receptacle.

The novel features that we consider characteristic of our invention areset forth with The vention itself, however, both as to its organizationand its method of operation, together with additional objects andadvantages thereof, will be understood from the following description ofspecific embodiments read in connection with the accompanying drawing,in which:

Figure 1 is a View in vertical section showing a clothes dryer includinga fuel burner control system in accordance with our invention;

4 Fig. 2 is a view in section taken along lines 11-11 of Fig. 1;

Fig. 3 is a circuit diagram of a fuel burner control system inaccordance with our invention;

Fig. l is a circuit diagram of a modification of our invention; and

Fig. 5 is a circuit diagram of another modification of our invention.

The apparatus shown in Figs. 1 and 2 comprises a container 55 in which aclothes tank '4 is mounted rotatable. The tank I is mounted at an angleto the vertical walls of the container and is provided with a neck iiwhich extends through an opening H in a slanting portion of the top ofthe container. This opening is cov ered by a door l5 which may bepivoted to the open position. Clothes may be inserted in the tan 7 afteropening the door.

The tank is rotated from an electric motor I? and as it is rotated, warmair flows over a portion of its surface and in dryers of some designscirculates within the tank 1. This air derived from a flue It in thelower region of the container 5. Near one end of the flue, a fan 21driven from the motor 17 rotates. The fan draws air from an opening 23in one side of the due and passes the air round a gas flame 25. The gasfor the flame is derived from a conductor 21 provided with a suitablevalve 29. The operation of the valve is controlled from a flame controlunit 3|.

A circuit diagram of our preferred flame control system is shown in Fig.3. This system comprises an electric discharge device 33 of thedirectly-heated hot-cathode type. The discharge device includes an anode35, a filament 3i, and a control grid 38. i It may be a triode or apentode, such as a 3A4.

The discharge device 33 is energized from the line conductors i! and 43of a supply which may be of the usual commercial 116 volt, Sal-cycletype. its anode 35 is connected to line conductor 23 through theexciting coil of a relay 4. The filament 37 of the discharge device isconnected at one terminal to the line conductor 43 through a potentialdrop resistor 45; at the other terminal it is connected through aresistor 3, a conductor 49 to one of the normally open contacts ill of apush button 53. The other of the normally open contacts is connected toline conductor 4|. he grid 39 or the discharge device is connected tothe junction of the bias resistor and the conductor :39 through a gridresistor 55. The heating current which flows through the filament 3?produces a drop across the bias re.- sistor 4''! which is impressedbetween the grid and the filament through the grid resistor 55 andfunctions as a bias normally maintaining the discharge device 33non-conductive.

The control grid 39 is also connected to a flame probe As in the systemdisclosed in the abovementioned copending application to Nagel, anignition assembly 5Q functions as a second flame probe.

In accordance with the preferred practice of our invention, the screengrid 58 of the discharge device, if a discharge device having a screengrid is utilized, should be connected to the line conductor 43 to whichthe anode 35 is connected through the exciting coil of the relay 44rather than directly to the anode. This connection improves thestability of the operation of the system.

To initiate the operation of the system, the push button 53 is actuated,closing the abovetraced circuit through the filament 31 of the dischargedevice as. The element, in a short t ime interval, rises to a propertemperature for'emis sion. The 'actuationo'f the push button '53 alsocloses an energizing circuit through the solenoid 6| of the "gas valve29. The 'lattercircuit extends from the upper line conductor "41 through"the now closed contacts 5i, the conductor 4-9,'the solenoid '61 to thelower line conductor 43. The gas valve 29 accordingly opens and gas issupplied to the burner 53. The actuatiohof the push button also closesthe ignition circuit "for the burner. This circuit "eitehds from line'con ductor 4!, through now closed contacts 51, normally closed contacts63' of the relay '44, the exciting coil of the ignitor'59, the vibratoryroute and cooperative shell 61 or the igniusr to the lower lineconductor 43. 'Thei'gnitor'2'9 operates in the same manner as a doorbelli'ts vibratory rod '65 repeatedly breaking 'the ignitor circuit at thejunction between this rod and .the shell "61 and producing an are at-the breach. "The arc fires the gas. While the ignitor 29 is operating,it produces a soft buzz which assures the operator that the system is inproper operation.

Once the flame 25 is ignited, the impedance between the ignitor shellfiland theflame probe 51 connected to the grid 39 decreases to .amagnitude of the'order of -20 or 30 megohms. .A 'small current flowsfrom line conductor 43 through the flame 25, grid resistor '55,conductor 49, contacts 5| to line-conductor. "A potential drop of theorder of several volts appears across the grid resistor 55. The latterpotential :is of a; polarity such that it counteracts the :biaspotential supplied through thebias resistor 41 "and th discharge devicebecomes conductive. The relay 44 is actuated and itsnormally-closedcontacts 53 are opened and normally iopencontacts 13close establishing a shunt across the TCOIItaCtS 5| of "dicator glowtube 15, a resistor TI, the exciting coil, rod 65 and shell 51 ofignitor 59 'to lower line conductor 43. The tube 15 is ignitedindicating that the system is in proper operation. Because the tube l5and resistor .71 are now in "circuit with the ignitor coil, the :currentflow through the coil is too small to actuate it.

On no longer hearing the buzz and onseeing the light 15, the operatorknows that the flame is ignitediand the system is otherwise in properoperation. She knows that she .may now release the push button 53. V

The system now remains in operation so long as the flame continues toburn. Should the flame 25 be accidentally blown out, the dischargedevice 33 becomes non-conductive, the relay 44 drops out and the gasvalve 29 immediately closes. Fluctuations in the flameimpedance of shortduration do not interrupt the operation of the system. The effect ofsuch fluctuations is suppressed by the condenser !9 connected inparallelwith the exciting coil of therelay 44.

.Asystemas shown in Fig.3,has the advantage that the'failure of itsmajor components causes the gas valve to close-that is, the system failssafe. If the filament 131 0: the discharge device should open, the flowof heating current to the 6. filament would be discontinued, the flov'i'of:p'l'a'te current through the discharged'evice 38 "would beinterrupted and the relay 44 would drop =out closing the-solenoid valve29 and shutting off-the gas. The solenoid valve 29 also is closed if therelay coil is short circuited or burned out orii the relay circuitisopened at anypoin't. 'Should one'of the flame probes -5l-'5l contact theother, the control grid 39 would be raised toa potential exceeding anodepotential and would deprive the anode-circuit of its normal current.Under such circumstances the relay i-4 may at 'oncedrop'out causing thegas valve '29 to close. If it fails to drop outtube 33 burns'out withina few seconds dropping out relay 44 and closing valve 29.

In a preferred system in accordance \vith'our invention which we haveconstructed and found to operate satisfactorily, the followingcomponents are included:

Power supply-commercial 110 volt,69-cycle type Electric discharge device533A'4 tube Relay 44standard type having a 5000. ohm impedance Condenserl94 microiarads Voltage drop resistor 451-100 ohm, 20 watt Biasresistor'41180 ohms, 5 watts Grid resistor 554.7 megohms.

temperature for emission, the heating potential supplied to the heaterinitially is higher than the rated potential. When the starting pushbutton of the system, shown in Fig. 4, is closed, it closes a supplycircuit across the primary 81 of a heating transformer through its uppernormallyopen contacts 99. Heating current is now supplied from thesecondary 9| of the transformer through the normally-closed contacts -53of the relay 44. The transformer 899I is so designed that the potentialsupplied to the heater 83 during this initial phase of the operation ofthe system exceeds the rated heater potential. Through the uppernow-closed contacts 89 of the push button '85, a circuit is also closedthrough the valve solenoid 6|. Through normally-open lower "contacts 93of the push button, a second circuit is closed through the exciting coilof the ignitor 59.

As in the system shown in Fig. 3, the discharge device (BI) ismaintained non-conductive. In the Fig. 4 system, the bias is suppliednot through a bias resistor but through the secondary 9| of the heatertransformer which is connected between the cathode 95 and the controlgrid 91 through the grid resistor 55. To accomplish this objective, thesecondary 9i must be so wound that its terminal which is connected tothe oathode is positive when the line conductor 4|, which is connectedto the anode 99 of the device, is positive.

Because the heater 83 is initially'supplied with a potentialsubstantially exceeding the rated potential, it is raised to a properlyemissive temperature within a short time interval of the order of fiveseconds after the push button 85 is closed.

During this time interval, a 'flame 25.is ignited.

The resistance between the flame probes 5'7 and impressed across thegrid resistor 5 counteracting the bias. The discharge device becomesconductive and the relay 44 is energized. The solenoid 8| and theprimary 8'1 are now maintained energized through the now-closed contacts13 of the relay 44 which shunts the con tacts 89' of the push button.The push button may now be released and when it is released the ignitioncircuit is broken. When the relay 44 is energized, its lowernormally-closed contacts 63 are opened, opening a shunt across a dropresistor in series with the heater 83. The potential across the heateris now reduced to the proper magnitude for long operating life.

The system shown in Fig. 4 now continues to operate in the same manneras the system shown in Fig. 3. As in the system shown in Fig. 3, thegrid resistor 55 may be of the order of 5 megohms and for this reasonthe electrode terminals of the discharge device and the components ofthe circuit need not be insulated for high impedance. As is the systemshown in Fig. 3, the system shown in Fig. 4 fails safe.

The system shown in Fig. 5 also includes an electric discharge device 8|having an indirectly heated hot cathode 95. In this system the cathodeheater 83 of the discharge device is supplied during steady stateoperation from the secondary 9| of the heater transformer ill-9|. Whenthe operation of the system is being initiated, the heater is suppliedfrom the main line conductors 4| and 43 through a parallel networkhaving as one branch the ignitor coil, rod 65 and shell 61; as a secondbranch the solenoid 6| and if necessary as a third branch a resistorI03. These components function to absorb a portion of the line voltagebut the net voltage impressed on the heater 83 is substantially greaterthan the rated heater potential.

When the initiating push button |05 is actuated, its uppernormally-closed contacts [01 are opened and its lower normally-opencontacts I09 closed. A circuit is now closed which extends from theupper line conductor 4| through the now-closed contacts I03 of the pushbutton, the secondary 9| of the heater transformer, the heater 83, aresistor |0|, the normally-closed contacts 03 of the relay 44, theparallel network consisting of the ignitor coil, the ignitor rod 05 andshell 61, the valve solenoid 5|, and the resistor |03, if one isnecessary, to the lower line conductor 43. Potential higher than therated potential is now supplied to the heater 83 and the latter israised to the proper emissive temperature in a short time interval. Theignitor 59 is, at the same time, energized and produces ignition sparkswhile emitting a buzzing sound. The gas valve solenoid BI is alsoenergized opening the valve 29 and permitting gas, to flow into theburner. The gas is ignited producing a flame 25. The decreased impedanceintroduced between the fiame probes 51 and 61 by the flame counteractsthe bias potential impressed in the grid circuit of the discharge device8| and the device to become conductive. The relay 44 is now energizedopening its normally-closed contacts 63 and closing its normally-openupper contacts 13.

At the now-open contacts 63, the ignitor circuit is broken. The buzzingsound stops.

The gas valve solenoid is now maintained energized in a circuitextending from the upper line conductor 4| through the novv-closed contacts 13 of the relay 44, the solenoid 6| to the lower line conductor43. The overvoltage heater circuit is broken at the now-open contacts 63of the relay 44. The system is now in complete operation.

When the normally-closed contacts 63 of the relay 44 are opened, a shuntacross a pilot lamp III is opened and the pilot lamp is energized in acircuit extending from the line conductor 4| through the now-closedcontacts 13 of the relay 44, the pilot lamp III, the exciting coil, rod65 and shell 61 of the ignitor 59 to the line conductor 43.

When the operator notes that the buzz has ceased and the indicator lightis on she knows that the system is in operation and releases the pushbutton I05. The primary 8'! of the heater transformer is now suppliedwith the potential in a circuit extending from the line conductor 4|,through the now-closed contacts 13 of relay 44, the normally-closedcontacts I01 of push button I05, the primary to the line conductor 43.The heater 83 is now supplied at the rated voltage from the secondary 9|through resistor |0|.

The system shown in Fig. 5 fails safe in the same manner as the systemshown in Fig. 3. If the heater 03 is burned out, the heater circuitopened, the anode circuit opened, or the relay 44 burned out or itscircuit opened, the discharge device 8| becomes non-conductive and thevalve 29 closes. If the flame probes become short circuited, substantialcurrent, flows between the grid 9'! and the cathode of the dischargedevice 8|. Under such circumstances the anode current may be reduced toa small magnitude such that the relay 44 at once becomes deenergized andthe gas valve 29 closes. If this event does not occur then the tube 8|burns out within a few seconds and relay 44 then drops out closing valve29.

The operation of the modifications of our system is entirely independentof the manner in which the power plug N3 of our system is inserted inthe supply receptacles. In explaining this feature of our system weshall assume that the line conductors 4| and 43 are connected throughthe plug I I3 to power company buses I I5 and Ill and that bus H1 isgrounded.

Consider the system shown in Fig. 3 and assume that the plug is insertedso that line 43 is connected to bus H5 and line 4| to bus At any instantwhen there is no flame in the burner and bus H5 is positive relative tobus III, the grid 39 and probe 51 are at ground potential, the cathode3'1 at a positive potential relative to ground and the probe 65 at thepositive potential of line |5. If a flame 25 is ignited positive currentflows from line 5 to ground through the flame and grid resistor 55producing a positive drop across the resistor to counteract the bias.Now assume that line 43 is connected to bus H1 and line 4| to bus H5 andconsider the system when there is no flame in the burner and line H5 isnegative relative to line Ill. The grid 39 and probe 57 are now at thenegative potential of the line 5, the cathode 31 is at a positivepotential equal to the bias and the probe 61 is at positive groundpotential. When a flame is now ignited positive current flows from lineto line 5 through the flame and grid resistor and the bias is againcounteracted.

The systems shown in Figs. 4 and 5 also opcrate in the manner describedabove.

While we have shown and described certain specific embodiments of ourinvention, we are fully aware that many modifications thereof arepracticable. Our invention, therefore, is not to be restricted exceptinsofar as is necessitated by claims.

We. 1311 31 1 45 our. invention:

In. comb nation. accntrol circu ti clud g a u rent-responsive. m chanismand. an; electric discharge device, havinga hot cathode, for controllinghe flow of current. hro h. said mechanism;. a..fir;st.circuit for,supplying heating currentexceeding the. heating. current rating, of sa ddevice, to said. catho.de.; a second circuit for sunplying heating,current. of a. ma nitude substantiallyequal, to. the. heating currentrating of said device; a. manually-actuable switch, of the type thatremainscl sed only so long. as. it is, manually actuated for, closingsaid. fir t. circuit and a switch ac u ble by said mechanis f r op n.-ing said, firstcircuit and closing said s d. 11,- cuit, and, formaintaining said first, circuit open andsaid second circuit, closed on.release, of said manually-.actuable switch.

2... In, combination, a. control circuit including a relay. and anelectricdischargedevice, havin hot cathode, for. controlling the flow ofcurrent through said. relay; a first. circuit for supplying heating currnt. exceeding the hea ng. c rr n rating of said, device to said,cathode; a second circuitfor supplying, heating current, of a magnitudesubstantially equal tothe heating current rating of said device; a.pushbutton of the type-that. remains closed, only so long as it ishaving an: anode; and: a cathode, terminals.

adapted: tobeconnected to. a commercial supply of 115 volts nominalrating, connections between said anodersaid" cathode and said terminals,a, circuitv for, heating said cathode including in series saidterminals, a voltage-drop impedance and said cathode, amanually-actuable switch for closing said circuit and another switchresponsive to the conductivity of said device for shunting out. saidmanually-actuable switch.

5; In; combination. an electric discharge device having: ananode andacathode of the directlyheated type, terminals adapted, to be connectedto: a power sunp'ly having a potential output of a magnitude exceeding;heating; potential rating of said cathode, connections between saidanode, said cathode and said terminals, a circuit 10 rent... exceeding.he hea ing cu rent rat ng, of said device, to said' cathode; a second"circuit inluding, sa d, norma lyl e contacts, for unplying, heatingcurrent to said cathode, substantially equal to the heating-current.rating of said device; and a switch actuable by the manual ac,- tuationof, said manually-actualole switch, for

opening saidfirst circuit, and, on release of said anism, aneiectrically-actuable component. for

initiating flow or current through said mechan in arnanually-actuableswitch of thetypethat remainsclosed, only. so long as it is manually ac-.tuated having a, first set of normally-open contacts and a secondset cfnormally-open, contacts;

.a first circuit adapted to be closed by said' first set'ofnormally-open contacts, for supplyingheati s current, exceedin he. h -cn r ing of, said; device, to said cathode; a second circuit forsupnlyinehea ine ur a d, t ode, substantially equal to theheating-current ratin of sa d dev c a ird c n udi said second set. of;normal yp n a s. tor upplyin curr nt. o sa d. c mp nt; and a switchactuable by thernanual actuation of said manually-actuable switch foropening said first circuit and closing said second circuit and formaintaining saidfirst circuit open andsa di se ond circuit. closedorrrelease of said manuallyactuable. switch.

8. In. combination, a control circuit, including acurrent-responsiuemechanism and an electric discharge device, having a hot cathode forcontrolling the flow, of, current through said mechanism; a. manuallyactuable switch of the type that .rernainsclosed only solong asit ismanually ac u ed. havin normally-c osed. and nor l yopen contacts;afirst. circuit, including said normally-open contacts, for supplyingheating current, exceedin g. the heating-currentratin of said device, tosaid cathode; a, second circuit, including. saidnormally-closedcontacts... S pp ying-heating currentto said cathodesubstantially equal to. the heating-current rating of said device; athird circuit including saidnorrnally-open contacts for su plyingheatingv current to said cathode substantially equal to. the heatingcur? rent; rating of said device; and. a switch actuable bythemanualactuation of said manually-ac,-

for heating said cathode including in series said terminals, a voltagedrop impedance and said cathode, a manually-actuable switch for closingsaid circuit and another switch responsive to the conductivity of saiddevice for shunting out said manually-actuable switch.

6. In combination, a control circuit including a current-responsivemechanism and an electric discharge device, having a hot cathode forcontrolling the flow of current through said mechanism; amanually-actuable switch of the type that remains closed only so long asit is manually actuated, having n-ormally-cloied and normallyopencontacts; a first circuit, including said normally-open. contacts, forsupplying heating curtuable switch for o ening said first circuit andclosing said third circuit so long as. said. man,-

ually-actuable switch remains, manually actuated and, on release ofsaid, manually-actuable, switch, open 1g said third circuit, and.closing said secand c rcui 9. In combination, a control circuitincluding an electric discharge device, having a hot cathode, amanually-actuable switch of the type that remains'cloeed only so long asit is manually actuated having normally-closed and normallyopencontacts; a first circuit, including said normally-open contacts, forsupplying heating current, exceeding the heating-current rating of saiddevice, to said cathode; a second circuit, including saidnormally-closed contacts, for supplying heating current to' said cathodesubstantially equal to the heating-current rating of said device; and aswitch actuable by the manual actuation of said manually-actuable switchfor opening said first circuit, and on release of saidmanfually-actuable switch, closing said second circuit.

'10. In combination, an electric discharge device of the type having ahot cathode which becomes properly emissive only after it has beenheated for a predetermined time interval by heating current of amagnitude equal to its current rating; a pair of terminals; atransformer having a primary and a secondary; a switch havingnormally-closed and normally-open contacts;

a relay responsive to the conductivity of said device having a singlemovable armature adapted to close normally-closed and normally-opencontacts; a first circuit including in series said normally-closedcontacts of said switch, said secondary and said cathode; a secondcircuit including in series said terminals, said normallyopen contactsof said switch, said cathode and said normally-closed contact of saidrelay; and a third circuit including in series said terminals, saidnormally-open contacts of said relay and said primary.

11. In combination, an electric discharge device of the type having ahot cathode which becomes properly emissive only after it has beenheated for a predetermined time interval by heating current of amagnitude equal to its current rating; an electrically-actuablecomponent for initiating a change in the conductivity of said device; apair of terminals; a transformer hav- .ing a primary and a secondary; aswitch having normally-closed and normally-open contacts; a relayresponsive to the conductivity of said device having a single movablearmature adapted to close normally-closed and normally-open con- .tacts;a first circuit including in series said normally-closed contacts ofsaid switch, said secondary and said cathode; a second circuit includingin series said terminals, said normallyopen contacts of said switch,said cathode, said normally-closed contact of said relay and saidcomponent; and a third circuit including in series said terminals, saidnormally-open contacts of said relay and said primary.

12. In combination, an electric discharge device of the type having ahot cathode which becomes properly emissive only after it has beenheated for a predetermined time interval by heating current of amagnitude equal to its current rating; a solenoid for initiating achange 'of said switch, said secondary and said cathode; a secondcircuit including in series said terminals, said normally-open contactsof said switch, said cathode, said normally-closed contact of said relayand said component; a third circuit including in series said terminals,said normallyopen contacts of said relay and said primary; a fourthcircuit including in series said terminals, said normally-open contactsof said switch, said cathode and said solenoid; and a fifth circuitincluding in series said terminals, said normallyopen contacts of saidrelay and said solenoid.

13. In combination, a control circuit including a current-responsivemechanism and an electric discharge device, having a hot cathode, forcontrolling the fiow of current through said mechanism; a transformerhaving a primary and a secondary for supplying heating current to saidcathode; a first circuit in shunt with said primary and including saidcathode for supplying heating current exceeding the heating currentrating of said device to said cathode; a second circuit including saidsecondary for supplying heating current of a magnitude substantiallyequal to the heating current rating of said device; a manually-actuableswitch for closing said first circuit and a switch actuable by saidmechanism for closing said second circuit.

14. In combination, a control circuit, an electric discharge devicehaving a cathode which becomes properly emissive only after it has beenheated for a predetermined time interval by heating current of amagnitude equal to its heating current rating; terminals for connectionto a potential supply; a heater transformer for said cathode having aprimary adapted to be connected to said terminals and a secondaryconnected to said cathode; a manually-operable witch for connecting saidterminals and said cathode in series and a switch actuable in responseto the conductivity of said device for in eifect disconnecting saidterminals from said cathode and connecting said terminals to saidprimary.

MORTIMER A. SCHULTZ.

GEORGE W. NAGEL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

